Various unsaturated C.sub.5 -hydrocarbons are useful as monomers for polymerization into a variety of useful polymers. Isoprene and piperylene are examples of C.sub.5 -hydrocarbon monomers that are frequently utilized in the synthesis of a variety of synthetic rubbers. Unfortunately, unsaturated C.sub.5 -hydrocarbon streams are often contaminated with cyclopentadiene (CPD). The presence of cyclopentadiene in C.sub.5 -hydrocarbon streams is very undesirable since cyclopentadiene is harmful to Ziegler catalysts, Szwarc catalysts, and ionic catalysts. Thus, the presence of cyclopentadiene in a C.sub.5 -monomer is detrimental to many of the catalysts commonly employed to polymerize such C.sub.5 monomers. For example, cyclopentadiene poisons the titanium catalysts commonly used to polymerize isoprene into polyisoprene.
Many techniques are known for the purification of organic compounds. One of the most widely used of these purification techniques is fractional distillation. However, fractional distillation cannot generally be employed to effectively separate cyclopentadiene from unsaturated C.sub.5 -hydrocarbons. This is because cyclopentadiene forms azeotropes with unsaturated C.sub.5 -hydrocarbons, for instance, isoprene.
Other more sophisticated techniques for the purification of organic compounds are also known. For example, U.S. Pat. No. 3,647,913 discloses a process for purifying olefinic hydrocarbon streams containing acetylenes and cumulative diolefins as impurities. This technique involves selectively polymerizing the acetylenes and cumulative diolefins in the hydrocarbon stream into solids by contacting them with a two-component catalyst system wherein the first component is a compound of a metal of Group IA, IIA, IIB, or IIIA, and wherein the second compound is a compound of a transition metal of Group IVB, VB, VIB, VIIB, or VIII of the Periodic Table. However, this patent does not specify a technique for the removal of cyclopentadiene from an unsaturated C.sub.5 -hydrocarbon. In fact, the catalyst disclosed by this reference cannot generally be used to polymerize cyclopentadiene into a solid.
U.S. Pat. No. 4,009,126 describes a technique for removing acetylenic impurities from organic compounds utilizing a zinc ferrite catalyst composition.
U.S. Pat. No. 4,035,433 describes a technique for the removal of acetylenic impurities from olefinic hydrocarbon streams by selective oxidation using a copper chromite catalyst.